Ecological regulation of algae in Middle Route of South-to-North Water Diversion Project
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Abstract:
Ecological regulation is one of the major prevention and control measures,and flow velocity is the key control variable.There is no online reservoir in the main canal,so it is prone to interfere with the normal water delivery downstream,and the hydraulic transition time is long in the process of ecological regulation.Currently,few implementation methods of ecological regulation are put forward. Based on the engineering characteristics of the main canal,the implementation strategy of ecological regulation was proposed by setting up its storage region to isolate the impact of ecological regulation on the downstream.The efficient canal pool operation method was adopted to reduce the repeated adjustment of the storage during ecological regulation.Considering the requirements of safety,speed,and stability,the implementation process and method of ecological regulation were set.The main canal was divided into flow velocity control region,storage regulation region,and normal operation region.The ecological regulation process was divided into the water filling stage and the discharge stage.The implementation steps of ecological regulation were given,including delineating the canal region,calculating the target flow of each gate in the velocity control region and the storage regulation region.Based on a one-dimensional unsteady flow simulation model of the canal,the duration of the flow increase stage and the duration of the flow decrease stage in the water filling stage were calculated.Thereafter,the flow control scheme of the velocity control region in the water filling stage was determined.The flow control scheme was input into the one-dimensional unsteady flow simulation model to judge the water level peak of each canal pool,if the safety requirement canal pool in the regulation region would be extended to downstream.After the duration of the discharge stage and the change value of the flow control of each gate in the discharge stage were calculated,and the discharge flow control scheme of the discharge stage was determined.The water filling flow control scheme and discharge flow control scheme meeting the conditions were taken as the gate group control scheme. Taking the operation of the main canal in March 2018 as a case study,a one-dimensional unsteady flow numerical simulation of algae ecological regulation was carried out.The results showed that the ecological regulation of 15 canal pools in the upper reaches of the main canal could be implemented within 3.5 days,and the flow velocity increased from about 0.4 m/s to about 0.7 m/s for more than 2 h.The water level changed smoothly and met the safety threshold requirements,and the flow in the normal operation region was not affected evidently. The proposed ecological regulation strategy and implementation method can achieve the velocity control goal along with ensuring the operation safety of the interference propagation to the downstream and reducing the hydraulic transition process.It can be used for not only algae control but also sediment deposition removal,aquatic biological attachment removal,and other velocity control scenarios.
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